Aramid nanofiber and modified ZIF-8 constructed porous nanocomposite membrane for organic solvent nanofiltration

Abstract

Highly cross-linked dense structure of integrally skinned asymmetric (ISA) organic solvent nanofiltration (OSN) membranes limits the permeability of organic solvent. Herein, a new porous nanocomposite OSN membrane was constructed based on one-dimensional nanofibers and a modified zeolitic imidazole framework, ZIF-8. Aramid nanofibers (ANFs) were exfoliated from Kevlar fiber in potassium hydroxide (KOH)/dimethyl sulfoxide (DMSO). The coordinative binding of branched polyethyleneimine (BPEI) on ZIF-8 surface gave rise to a good dispersion of ZIF-8 in the ANFs dope solution. The membrane was prepared by non-solvent induced phase inversion and thermal post-treatment. The effect of ZIF-8 on membrane physicochemical properties was inferred by SEM, XRD, AFM, FTIR, TGA, contact angle analysis and tensile strength measurement. The results demonstrated that the ZIF-8 intercalated among ANFs and produced a porous nanofibrous network. The porosity of the membrane increased from 23.3% to 56.9%. As consequences, the prepared ANF nanocomposite membrane showed two times higher permeances for polar (methanol, ethanol, isopropanol, acetone, tetrahydrofuran) as well as non-polar solvents (hexane, carbon tetrachloride) than that of the pristine membrane. It was found that the nanocomposite membrane has promising applications in nanofiltration of organic liquids for molecular separation. The long-term OSN filtration showed that the membrane had an ethanol and isopropanol permeance of 2.9 L m−1 h−1 bar−1, 1.8 L m−1 h−1 bar−1 respectively, with erythrosin B (EB, 836 g mol−1) rejections over 90%. The architecture of one-dimensional nanofibers and porous nanomaterials provides a new route for fabrication of nanocomposite OSN membranes.